JP3448461B2 - Optical fiber type dispersion compensator - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a single mode optical fiber having a dispersion of zero in a 1.3 μm band as a transmission line, and combines it with an erbium (Er) -doped fiber amplifier.
The present invention relates to an optical fiber type dispersion compensator for performing dispersion in a 55 μm band and compensating for dispersion in a system that increases the transmission capacity of the transmission line.

[0002]

2. Description of the Related Art Two factors, an optical fiber loss characteristic and a dispersion characteristic, are major obstacles in increasing the speed and bandwidth of a long-distance optical transmission system. Regarding the dispersion characteristics among these obstacles, a single mode optical fiber in which modal dispersion is removed has been developed and adopted. As this single-mode optical fiber, a silica-based optical fiber in which germanium is added to the core and which has a step-type refractive index distribution is generally used. This optical fiber has zero dispersion in the 1.3 μm band,
The loss is the smallest at wavelengths around 1.55 μm.

On the other hand, as an amplification to be incorporated in a system for transmitting an optical signal, an optical amplifier using an optical fiber doped with erbium (Er) in a core, which operates at a wavelength around 1.55 μm (erbium (Er) -doped fiber amplifier). )
Has been developed, amplification of optical transmission has become extremely easy, and system capacity can be increased economically. Therefore, the problem of loss is solved by transmitting an optical signal in the 1.55 μm band. As described above, the dispersion of the single-mode optical fiber is zero in the 1.3 μm band, and the dispersion occurs in the 1.55 μm band. Therefore, 1.5
By improving the dispersion characteristics in the 5 μm band, long distance, high speed,
Since wide band transmission is possible, various improvements in dispersion characteristics have been made. Additivity holds for dispersion characteristics. Therefore, it is possible to improve the dispersion characteristics by connecting an optical fiber of the opposite sign to the single-mode optical fiber for the transmission line to the single-mode optical fiber, and such a method is simple and highly reliable, Attention has been paid. Moreover, this dispersion compensating method is extremely practical because it can be solved by applying a manufacturing technique for manufacturing a dispersion compensating optical fiber for compensating for dispersion.

The dispersion compensating optical fiber is treated as one component, that is, an optical fiber type dispersion compensator. Therefore, as a dispersion compensating optical fiber, the characteristics such as loss of the transmission line to be inserted do not deteriorate, and the size is made as small as possible (shortening the length) so that it does not occupy a space for use in a repeater. In order to satisfy these conditions, it is desired that the absolute value of dispersion is large.
The dispersion value of an optical fiber is the sum of the values of material dispersion and structural dispersion. Of these, the material dispersion has a positive value and has little dependence on the refractive index distribution. Therefore, as the dispersion compensating optical fiber, a desired refractive index distribution characteristic can be obtained by selecting a refractive index distribution having a large negative structural dispersion. An optical fiber for dispersion compensation can be obtained. As an optical fiber having such a refractive index distribution, several refractive index distributions have been proposed, as one example is described in JP-A-6-11620. As an optical fiber type dispersion compensator, such an optical fiber is coiled into a small diameter or wound on a small reel and housed in a housing for holding, and a single mode type optical fiber is placed at both ends of the dispersion compensating optical fiber. It is modularized by installing a pigtail optical fiber that connects to the fiber with low loss.

[0005]

As one of the performance indexes of the dispersion compensating optical fiber, the FOM value (Figure of
merit: a value obtained by dividing the dispersion value at the transmission wavelength by the loss value at the transmission wavelength, ps / nm / dB) is used. This FOM value indicates how much power penalty there is when compensating for a predetermined amount of dispersion, and the larger the FOM value, the smaller the loss and the better. In other words, F
A large OM value is advantageous because the incident power with respect to the amount of dispersion to be compensated for is small. On the other hand, in consideration of further speeding up of the transmission system, it is desirable that the dispersion characteristics compensate not only the absolute value of dispersion but also the dispersion slope. For this purpose, "the value obtained by dividing the dispersion slope at the transmission wavelength by the dispersion value at the transmission wavelength" (hereinafter referred to as "dispersion slope-dispersion ratio") is the dispersion of the single-mode optical fiber that constitutes the transmission line. It is required to be approximately equal to the slope-dispersion ratio.
A dispersion compensating type optical fiber for dispersion compensation that can compensate not only the dispersion value but also the dispersion slope can be obtained by optimizing the refractive index distribution of the optical fiber.
1620, JP-A-7-79719, and JP-A-7-261048.

[0006]

[Problems to be solved] In a transmission system, F
The OM value is not only an evaluation criterion for dispersion characteristics, but also an index for another important evaluation characteristic. The FOM value is better as the absolute value of the variance is larger and the loss value is smaller. For that purpose, the absolute value of dispersion should be large and the loss should be small. On the other hand, since the dispersion compensating optical fiber is housed in a transmission device for use, it is required to be processed into a compact shape, and it is wound on a small reel to be modularized. However, the transmission loss characteristic of the optical fiber is relatively weak against bending, and if the transmission loss increases due to the winding process, the FOM
As a result, the value decreases. The change in transmission loss due to bending of the optical fiber depends on the structure of the optical fiber. Since this increase in transmission loss correlates with the dispersion characteristic, prioritizing the dispersion characteristic should use a dispersion compensating optical fiber that is resistant to bending. Can not be.

Optical fibers having a negative dispersion characteristic include those that shift the zero-dispersion wavelength of a dispersion-shifted fiber to the longer wavelength side, those that have a high relative refractive index difference, those that have a W-type refractive index distribution, and segments. A type having a refractive index distribution is known. The dispersion compensating optical fiber with and has a matched type refractive index distribution (hereinafter referred to as the matched type) and has a positive dispersion slope like the single mode optical fiber. The absolute value of increases, and the FOM value increases accordingly. However, when the addition amount of germanium is increased to increase the relative refractive index difference, abrupt deterioration of loss starts beyond a certain range, and the FOM value decreases although the dispersion slope tends to increase. On the other hand, it becomes stronger against deterioration of the transmission loss value due to bending. Therefore, although the matched type dispersion compensating optical fiber with this is strong against bending, the absolute value of dispersion cannot be increased, and it is difficult to increase the FOM value. The dispersion-compensating optical fiber of and has a negative dispersion gradient because it has a structure having a low refractive index depressed layer between a high refractive index layer and a medium refractive index layer. There is a drawback that the stability of loss is inferior to that of the matched type refractive index distribution. The dispersion compensating optical fiber having a depressed layer like the W-type refractive index distribution can increase the absolute value of dispersion (negative dispersion value) from the characteristics of structural dispersion, but approaches the conditions for increasing the absolute value of dispersion. A large amount of light propagating into the clad leaks into the cladding, and the bending loss edge on the long wavelength side is close to the used wavelength, and bending causes an increase in transmission loss. As described above, the dispersion compensating optical fiber having the structure having the depressed layer has a small transmission loss in the state where strong bending is not applied, and FO
Although the M value is large, when it is wound on a reel for modularization, the transmission loss value is deteriorated and the FOM value becomes insufficient. Therefore, it is difficult to manufacture an optical fiber for dispersion compensation that satisfies both extremely large dispersion characteristics and stable transmission loss characteristics with these optical fibers for dispersion compensation and gives a good FOM value after modularization. As a countermeasure against this, it is conceivable to increase the winding diameter, but there is a problem that the volume becomes large and the storage becomes difficult.

In order to compensate the dispersion gradient, the FOM value before modularization becomes a problem. That is, when a negative dispersion gradient is applied to the dispersion compensating optical fiber, the wavelength at which the gradient becomes steep is different from the wavelength at which the maximum value of dispersion is given.
Attempting to fully compensate for the dispersion slope will result in an insufficient FOM value. It is also possible to adjust the refractive index distribution to prepare a dispersion compensating optical fiber that satisfies both the dispersion gradient compensation characteristic and the FOM value corresponding to each system.
It is practically impossible to design and manufacture an optimum dispersion compensating optical fiber for each application. In addition, the deterioration of the transmission loss characteristic becomes a problem when modularizing. In particular, in order to obtain a negative dispersion slope, it is necessary to have a structure with a depressed layer around the core.The dispersion compensating optical fiber with this depressed layer causes an increase in transmission loss due to bending as described above. Characteristics deteriorate. Therefore,
In modularization, it was not possible to wind the coil on a small coil or a reel with a small body diameter, and there was a drawback that the module could not be made small.

[0009]

SUMMARY OF THE INVENTION The present invention provides an optical fiber type dispersion compensator which exhibits negative dispersion and has a large FOM value at a low cost. Is 1.
Dispersion becomes zero in the 3 μm band, and it is connected to a single mode optical fiber having a positive dispersion in the 1.55 μm band.
In an optical fiber type dispersion compensator inserted into an optical fiber line so that the total dispersion in the 55 μm band becomes almost zero, a plurality of dispersion compensating optical fibers having a negative dispersion value and a transmission loss characteristic depending on a bending radius. Using bending
Start of winding of dispersion compensating optical fiber on the side with strong transmission loss characteristics
Dispersion compensating light on the side where the transmission loss characteristic due to bending is weak
The optical fiber type dispersion compensator is characterized in that it is smaller than the fiber and is wound from the inside to the outside .

According to a second aspect of the invention, the transmission loss characteristic due to bending is
Dispersion-compensating optical fiber, which has a weak property, has a characteristic of transmission loss due to bending.
The FOM value is larger than that of dispersion-compensating optical fiber with strong characteristics.
An optical fiber-type dispersion compensator according to claim 1, wherein the decoction.

According to a third aspect of the present invention, the dispersion compensating optical fiber constituting the dispersion compensator has a negative dispersion slope and a dispersion slope-dispersion ratio, that is, the dispersion slope at the transmission wavelength is represented by the dispersion value at the transmission wavelength. 3. The optical fiber type dispersion compensator according to claim 1, wherein the divided value is substantially equal to or larger than the dispersion slope-dispersion ratio of the single mode optical fiber.

[0012] In the invention described above, on one reel (bobbin) wound transmission loss characteristic strong dispersion compensating optical fiber according to bend inwardly, the transmission loss characteristic for not dispersion compensating weak by sequentially bending thereon You may wind the optical fiber into a module, or prepare multiple reels with different barrel diameters and wind the dispersion compensating optical fiber with a large bending loss on a reel with a small barrel diameter. The weak dispersion compensating optical fiber may be wound on a reel having a large barrel diameter to form a module.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. In the present embodiment, the method for obtaining the length of each dispersion compensating optical fiber from the proportion of the total length of the dispersion compensating optical fiber for the purpose of compensating for dispersion is as follows. First, let D be the total amount of compensation dispersion required for a modularized dispersion compensating optical fiber.
_T (ps / nm), FOM value is FOM _T (ps / nm /
dB), the dispersion value of one of the dispersion compensating optical fibers MF1 is D ₁ (ps / nm), and the FOM value is FOM ₁ (ps /
nm / dB), the dispersion value of the other dispersion compensating optical fiber MF2 is D ₂ (ps / nm), and the FOM value is FOM ₂ (ps
/ Nm / dB). Here, when the ratio of D ₂ (ps / nm) to _DT (ps / nm) is r, 1 / FOM _T = (1-r) / FOM ₁ + r / FOM ₂ (1) The length of MF1 to be converted is L ₁ (km),
Assuming that the length of MF2 is L ₂ (km), r = D ₂ L ₂ / _DT ... (2). Therefore, from equations (1) and (2), L ₁ = ( _DT / D ₁ ) × (1-r) ··· (3) L 2 = (D T / D 2) × r ··· (4) is obtained. Therefore, the required fiber length is (3),
It can be obtained by the equation (4).

Further, in the present embodiment, when the module is modularized for the purpose of compensating for the dispersion and further compensating for the dispersion slope, the length calculated by the above equations (3) and (4) is obtained. It is necessary that each dispersion compensating optical fiber has a predetermined dispersion slope. The method of obtaining this dispersion gradient is as follows. First, the total compensation dispersion gradient amount required for the modularized dispersion compensating optical fiber is S
_T (ps / nm ² / km), dispersion slope of MF1 to S
₁ (ps / nm ² / km), the dispersion slope of MF2 is S
₂ (ps / nm ² / km), the dispersion value of the compensation target single mode optical fiber is D _s (ps / nm), and the dispersion slope is S _s
(Ps / nm ² / km), the length of all routes after the dispersion compensator is inserted is L _r (km), and the dispersion slope is S _r (ps / nm)
² / km), the residual dispersion value of all routes after insertion of the dispersion compensator can be set to 0 (ps / nm) by satisfying D _S × L _r + D _T = 0 (5) . Here, the root dispersion gradient S _r (p
s / nm ² / km) is S _r = S _s + (S ₁ × L ₁ + S ₂ × L ₂ ) / L _r (6). Since L ₁ and L ₂ are obtained by the above equations (3) and (4), S ₁ and S ₂ may be obtained so that S _r becomes 0 (ps / nm).

[0015]

EXAMPLES Example 1 An example in which matched type dispersion compensating optical fibers are combined will be described. In the case of a matched type (simple step type) dispersion compensating optical fiber as shown in FIG. 1, the larger the relative refractive index difference (hereinafter referred to as Δ) between the core and the clad, the larger the negative dispersion value. That is, a dispersion compensating optical fiber having negative dispersion and a large absolute value of dispersion can be obtained. However, generally in a silica optical fiber, it is necessary to add a large amount of germanium in order to increase Δ, but if a large amount of germanium is added, the transmission loss value deteriorates due to Rayleigh scattering and the like. On the other hand, when Δ is small, it is difficult to increase the absolute value of dispersion, but the transmission loss is small. If the transmission loss is small, the FOM value will be large even if the absolute value of the dispersion is small. Dispersion compensating optical fiber of the matched type resistant to bending Among various refractive index distribution, also larger Δ is the in refractive index distribution of the matched type, transmission wavelength is strong against the bending closer to the cut-off wavelength Become. Therefore, in this case, since Δ is small, it is weak against bending, and when it is modularized, the transmission loss increases due to bending. Therefore, the dispersion compensating optical fiber having a large Δ (= strong in bending) is arranged inside and the dispersion compensating optical fiber having a small Δ (= weak in bending) is arranged outside so that the FOM value is deteriorated. Can be prevented.

A specific example is shown below. An example will be described in which two matched type dispersion compensating optical fibers are combined. In the two matched type dispersion compensating optical fibers used here, the core is silica glass (SiO ₂ —GeO ₂ ) doped with germanium, and the cladding is silica glass (Si
O ₂ ), Δ is 2.2% and 2.8, respectively.
%Met. Table 1 shows the characteristics of the two dispersion compensating optical fibers. In the following, MF with Δ of 2.2% is
An MF2 having 1 and Δ of 2.8% is called MF2.

[0017]

[Table 1] * The dispersion value, transmission loss value, and FOM value are all values at 1.55 μm.

MF1 and MF2 were wound on two types of reels having a winding width of 25 mm and a body diameter of 30 mm and 80 mm, respectively, and the transmission loss value and the FOM value were measured. When MF1 was wound on a reel with a barrel diameter of 30 mm, the transmission loss value increased and exceeded 0.70 dB / km, and the FOM value was less than 100 ps / nm / dB, but the barrel diameter was 80 m.
There was no change from the values in Table 1 when wound on a reel of m. The MF2 had no change in the transmission loss value when it was wound on either reel having a barrel diameter of 30 mm or 80 mm.
Here, when a module with a total compensation dispersion amount of 400 ps / nm was created, when the above two types of dispersion compensating optical fibers were separately modularized, MF2 had a large Δ and was resistant to bending, and thus MF2 was wound on the reel. The outer diameter (hereinafter referred to as the winding end diameter) was 140 mm, which was relatively small, but MF1 has a small Δ and is weak against bending.
The winding end diameter of No. 1 was 175 mm and could not be made smaller.

Therefore, 25% of the total length of the dispersion compensating optical fiber is MF2, and the remaining 75%.
As MF1, and after winding MF2 on a reel with a barrel diameter of 30 mm, MF1 is fusion-spliced at the end of winding, and MF1 is
A module was prepared by winding on F2. The completed module was able to suppress the FOM value to 190 ps / nm / dB and the winding end diameter to 155 mm. This is because the required length of the dispersion compensating optical fiber depends on the dispersion value that each has, so that the dispersion compensating optical fiber has a large negative dispersion (= negative dispersion and a large absolute value of the dispersion). That is, MF2 can achieve a large dispersion in a short length, and since MF2 has a large Δ and is strong against bending, the winding start diameter, that is, the barrel diameter can be set to 30 mm.

(Embodiment 2) An embodiment in which W-type dispersion compensating optical fibers are combined will be described. A dispersion compensating optical fiber having a W-type refractive index distribution as shown in FIG. 2, that is, a first core layer having a high refractive index and a second core having a low refractive index are sequentially arranged from the center.
In the case of a dispersion compensating optical fiber having a core layer and a cladding layer having an intermediate refractive index between the first core layer and the second core layer, a large structural dispersion is exhibited due to the contribution of the second core layer having a low refractive index, There is a drawback that transmission loss increases easily. In order to increase the FOM value of this dispersion compensating optical fiber, it is necessary to increase the absolute value of dispersion and reduce the transmission loss. The dispersion value is the refractive index ratio of the first core layer and the second core layer (hereinafter, RΔ), the core diameter ratio of the first core layer and the second core layer (hereinafter, Ra), and the core diameter (second core layer). Outer diameter) and so on. When RΔ is large, the absolute value of dispersion also increases, but at the same time bending loss easily occurs. To prevent this, the relative refractive index difference (Δ ⁺ ) with respect to the clad of the first core layer should be increased, but in order to increase Δ ⁺ , a large amount of germanium must be added and the transmission loss value deteriorates. Resulting in. The dispersion value also depends on the core diameter, and when RΔ and Ra are constant, the smaller the core diameter, the larger the absolute value of dispersion. However, in this case, transmission loss due to bending is likely to occur. Therefore, in order to obtain a dispersion compensating optical fiber in which the absolute value of dispersion is increased and the transmission loss value is not deteriorated, it is necessary to optimize RΔ and the core diameter and then appropriately suppress Δ ⁺ .

Therefore, the optimum structure was examined by appropriately changing these values. As an examination method, while adjusting the relative refractive index difference (hereinafter, referred to as Δ ⁻ ) of the second core layer with respect to the clad so that RΔ becomes 5.5, the relative refractive index difference of the first core layer with respect to the clad ( Hereinafter, the transmission loss and the dispersion value were evaluated by changing (Δ ⁺ ). At this time, the core diameter is the core diameter of the first core layer (hereinafter referred to as d ₁ ).
The optimum value was obtained by changing the range of 2.0 to 2.5 μm and Ra2 to 4. The evaluation result is shown in FIG.

As shown in FIG. 3, the absolute value of the variance is Δ⁺of
Although it increased with the increase, the transmission loss value is Δ⁺Is 2.
If it is less than 1% or greater than 2.7%, the transmission loss value will be sharp.
It has grown dramatically. This is Δ⁺Is less than 2.1%, light
Since the part that meets the conditions for power transmission is narrow,
This is because it was impossible to optimize the diameter and Ra. ⁺
Is larger than 2.7%, the transmission loss increases rapidly.
This is due to the high concentration of germanium added. Note that Δ
⁺The FOM value in the range of 2.1% to 2.7% is
It was about 220 to 240 ps / nm / dB. Also Δ
^-Is less than −0.5%, transmission loss increases due to bending.
Transmission loss deteriorates to 1 dB / km, and Δ^-But
-If it is more than 0.3%, sufficient RΔ cannot be obtained and dispersion is lost.
Both FOM values are small because the logarithmic value becomes small.
It's gone. Therefore, the optical fiber type of this structure
The dispersion compensating optical fiber in the dispersion compensator is composed of the first core layer.
Difference in relative refractive index with respect to the cladding layer Δ⁺2.1% or more 2.
7% or less, and the ratio of the second core layer to the clad layer
Refractive index difference Δ^-Is set to -0.5% or more and -0.3% or less.
To provide a superior optical fiber type dispersion compensator
You can

A specific example is shown below. A case where two W-type dispersion compensating optical fibers are combined will be described as an example. In the two W-type dispersion compensating optical fibers used here, the first core layer is silica glass (SiO ₂ —GeO ₂ ) doped with germanium, and the second core layer is silica glass doped with fluorine (SiO ₂ -F), the clad is made of quartz glass (SiO ₂ ), and Δ ⁺ is 2.2% each
And 2.8%. Table 2 shows the characteristics of the two dispersion compensating optical fibers. In the following, the one with Δ ⁺ of 2.2% is called DF1 and the one with Δ ⁺ of 2.8% is called DF2.

[0024]

[Table 2] * The dispersion value, transmission loss value, and FOM value are all values at 1.55 μm.

DF1 and DF2 were wound on two types of reels having a winding width of 25 mm and a body diameter of 30 mm and 80 mm, respectively, and the transmission loss value and the FOM value were measured. When DF1 was wound on a reel with a barrel diameter of 30 mm, the transmission loss value increased and exceeded 0.70 dB / km, and the FOM value was less than 150 ps / nm / dB, but the barrel diameter was 80 m.
There was no change from the values in Table 2 when wound on a m reel. The transmission loss value did not change when DF2 was wound on either reel having a barrel diameter of 30 mm or 80 mm.
Here, when making a module with a total compensation dispersion amount of 400 ps / nm, if the above-mentioned two types of dispersion compensating optical fibers are individually modularized, DF2 has a large Δ ^{+ and} is strong against bending, so the winding end diameter of DF2 is Although it was possible to make the size relatively small as 110 mm, since DF1 has a small Δ ^{+ and} is weak against bending, the winding end diameter of MF1 was 150 mm, and it could not be made smaller.

Therefore, the dispersion compensating light is modularized.
Of the fiber, 25% of the total length is DF2 and the remaining 75%
Is DF1, and DF2 is wound on a reel with a body diameter of 30 mm.
Later, DF1 is fusion-spliced to the end of winding, and DF1 is
A module was prepared by winding on F2. Done
The module has a FOM value of 220 ps / nm / dB, winding
The end diameter could be suppressed to 125 mm. this
Is the required length of the optical fiber for dispersion compensation.
Has a large negative variance value (= negative
For dispersion compensation and has a large absolute value of dispersion)
Optical fiber, that is, DF2, obtains large dispersion in a short length
That DF2 is Δ ⁺Has a large bend
Since it is strong against winding, the winding start diameter, that is, the body diameter should be 30 mm.
It was achieved by being able to do.

(Embodiment 3) A W-type dispersion / dispersion compensation optical fiber in which a dispersion-gradient compensation-type dispersion compensation optical fiber and a high-dispersion-type dispersion compensation optical fiber are combined will be described. Japanese Patent Application No. 7-7971 discloses a negative dispersion gradient type dispersion compensating optical fiber for flatly compensating for dispersion.
As described in No. 9, Δ ⁺ is 1.6% to 2.1%.
The gradient compensation can be most appropriately performed with a structure having a refractive index distribution in which%, Δ ⁻ are −0.6% to −0.45%. Therefore, in the present embodiment, Δ ⁺ is 2.0%,
An optical fiber for dispersion compensation (hereinafter referred to as DC1) having Δ ⁻ of −0.55% and Ra of 2.5 was manufactured. Further, by increasing Δ ⁺ further, a dispersion compensating optical fiber (hereinafter referred to as DC2) having a large FOM value and strong against transmission loss against bending was manufactured. Table 3 shows the characteristics of the two dispersion compensating optical fibers.

[0028]

[Table 3] * The dispersion value, transmission loss value, and FOM value are all values at 1.55 μm.

The characteristics when DC1 and DC2 are combined are shown in FIG. Although the FOM value decreases when DC1 becomes longer, 1.55μ by combining single mode optical fibers
The dispersion slope becomes smaller when the dispersion at m is compensated. DC
1 alone is overcompensated, and the total gradient is negative. Among the dispersion compensating optical fibers that are modularized,
About 5% of the total length is DC2 and about 95% of the total length is DC1
When combined, the dispersion slope becomes zero. This is one of the effects of combining dispersion compensating optical fibers having different structures. How much the total gradient value is allowed depends on the system, but for example, when allowing 0.01 ps / nm ² / km, DC2 having a length of up to about 25% of the total length can be combined. In this case, the FOM value is 170p
It can be improved to s / nm / dB. Moreover, D
Since the absolute value of dispersion of C2 is larger than that of DC1, the length of the dispersion compensating optical fiber that is modularized can be shortened, and the increase in transmission loss due to bending is small, so that more compact storage is possible. .

Next, the winding method will be described. FIG. 5 shows an example in which the dispersion compensating optical fiber 1 that is weak against bending and the dispersion compensating optical fiber 2 that is resistant to bending are modularized. Figure 5 (a)
Is a generally shaped reel 15 (body diameter 65 mm, winding width 25 mm) with a dispersion-compensating optical fiber 2 strong against bending inside and a dispersion-compensating optical fiber 1 weak against bending.
Is wound on the outside. The dispersion compensating optical fiber 1 and the dispersion compensating optical fiber 2 are fusion spliced. For example, the dispersion compensating optical fiber 2 is DC1 of the third embodiment, and the dispersion compensating optical fiber 1 is D of the third embodiment.
When manufacturing a module with a total compensation dispersion amount of 700 ps / nm using C2, the dispersion compensating optical fiber 2 is 75%,
When the dispersion compensating optical fiber 1 is combined to have 25%, the dispersion compensating optical fiber 2 has a length of 5.83 k.
m, and the length of the dispersion compensating optical fiber 1 is 1.35 km. In this case, the winding end diameter can be set to 185 mm, and the winding end diameter of a module in which only DC1 is wound is 205 mm (from the relationship of transmission loss to bending, the body diameter 1
It was possible to have an outer diameter of about 90% of that wound on a 00 mm reel). This is because the required length of the dispersion compensating optical fiber depends on the dispersion value that each has, so that the dispersion compensating optical fiber has a large negative dispersion value (= negative dispersion and a large absolute dispersion value). That is, DC2 can obtain a large dispersion in a short length.
Since Δ ⁺ is large and strong against bending, it was achieved by being able to set the winding start diameter, that is, the body diameter to 65 mm. At this time, the transmission loss did not deteriorate, and the FOM value was 165 ps / nm / dB, which was almost the same as the calculated value.

In FIG. 5B, the dispersion compensating optical fibers 1 and 2 are wound around two reels 16 and 17 having different barrel diameters. For example, the dispersion compensating optical fiber 1 is wound around a reel 16 having a barrel diameter of 100 mm, a collar diameter of 205 mm, and a winding width of 19 mm, and the dispersion compensating optical fiber 2 is disposed at a barrel diameter of 65.
mm, collar diameter 205 mm, winding width 3.5 mm reel 17
Each is wound. The reel 16 and the reel 17 are attached to each other on the collar surface, and the total compensation dispersion amount is 700 ps /
The DC1 of the third embodiment is 5.83 km on the reel 16 and the DC2 of the third embodiment is on the reel 17 so as to form a module of nm.
Was wound for 1.35 km, the winding width could be about 90% of the winding width when the module was wound only with DC1. Further, since the dispersion compensating optical fiber 1 and the dispersion compensating optical fiber 2 are separately wound, there is no need to perform fiber connection in the middle of reel winding, so that work efficiency is also improved.

FIG. 5 (c) shows an example which is particularly effective when adjusting the characteristics of a small amount of dispersion compensating optical fiber. For example, this is an effective example in a case where the 95% dispersion compensating optical fiber 1 and the 5% dispersion compensating optical fiber 2 are combined, and one collar surface of one of the two reels 18 and 19 having different barrel diameters is the same. The dispersion compensating optical fibers 1 and 2 are integrated so as to exist on a plane and are wound. Here, the reel 18 has a body diameter of 65 mm, a collar diameter of the unintegrated side of 75 mm, and a winding width of 25 mm.
Is a body diameter of 100 mm, the collar diameter of the unintegrated side is 200
mm and a winding width of 25 mm. Total compensation dispersion amount 700ps
The DC1 of Example 3 is 7.39 km on the reel 19 and the D of Example 3 is on the reel 18 so as to form a module of 1 nm / nm.
When C2 was wound 0.27 km, a very small module could be manufactured.

In the embodiment of the present invention, both are 2
Although an example in which the dispersion compensating optical fibers are combined is shown, the number of dispersion compensating optical fibers combined in the present invention is not limited to two, and may be three or more. Also, the combination of dispersion compensating optical fibers is not limited to the example shown in the embodiment of the present invention.

[0034]

As described in detail above, in an optical communication network using a 1.3 μm band zero-dispersion single mode optical fiber as a transmission line, the characteristics are improved so as to enable long-distance, high-speed, wide-band optical transmission. It is possible to realize an optical fiber type dispersion compensator that is made and can be downsized.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a refractive index distribution of a matched type dispersion compensating optical fiber which is an embodiment of a dispersion compensating optical fiber used in an optical fiber type dispersion compensator according to the present invention.

FIG. 2 is a schematic diagram showing a refractive index distribution of a W-type dispersion compensating optical fiber which is an embodiment of the dispersion compensating optical fiber used in the optical fiber type dispersion compensator according to the present invention.

FIG. 3 is a schematic diagram showing characteristics of a W-type dispersion compensating optical fiber which is an embodiment of a dispersion compensating optical fiber used in the optical fiber type dispersion compensator according to the present invention.

FIG. 4 is a schematic diagram showing characteristics when a dispersion flat compensation type fiber which is one embodiment of a module used for an optical fiber type dispersion compensator according to the present invention and a high negative dispersion compensation fiber are combined.

FIG. 5 is a schematic view showing an embodiment of how to wind an optical fiber for dispersion compensation in an optical fiber type dispersion compensator according to the present invention.

[Explanation of symbols]

Optical fiber for dispersion compensation 15, 16, 17, 18, 19 reels

Continuation of the front page (56) Reference JP-A-8-84135 (JP, A) JP-A-8-50208 (JP, A) JP-A-6-11620 (JP, A) JP-A-10-31120 (JP , A) Structural Design and Modulation Technology of Dispersion Compensating Optical Fiber, Technical Report of IEICE, Japan, 1995, Vol. 95 No. 96 (CS95 41-55), 87-94 (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 6/00-6/44 396

Claims (3)

(57) [Claims] 1. Dispersion becomes zero in the 1.3 μm band, and 1.55
An optical fiber connected to a single mode optical fiber having a positive dispersion in the μm band and inserted into an optical fiber line so that the total dispersion in the 1.55 μm band becomes almost zero.
-Type dispersion compensator uses multiple dispersion compensating optical fibers whose dispersion value is negative and whose transmission loss characteristics depend on the bending radius .
The optical fiber for dispersion compensation on the side with strong transmission loss characteristics due to bending
The fiber winding start diameter is weak and the transmission loss characteristics due to bending are weak.
Smaller than the optical fiber for dispersion compensation on the side
An optical fiber type dispersion compensator characterized by being wound from the inside to the outside . 2. A dispersion compensating light having a weak transmission loss characteristic due to bending.
A fiber is a dispersion-compensating light with strong transmission loss characteristics due to bending.
The optical fiber type dispersion compensator according to claim 1 , wherein the FOM value is larger than that of the fiber. 3. The dispersion compensating optical fiber constituting the dispersion compensator has a negative dispersion slope and a dispersion slope-dispersion ratio approximately equal to or greater than the dispersion slope-dispersion ratio of a single mode optical fiber. It is large, The claim 1 or 2 characterized by the above-mentioned.
An optical fiber type dispersion compensator according to.